As shown in FIG. 5, a roller bearing assembly includes: an inner ring 1; an outer ring 2; and a roller 3 as a rolling element rollably interposed between these inner and outer rings. The inner ring 1 is formed with a rib 4 which makes contact with an end face (greater end face) of the roller 3 for guiding the rolling motion of the roller 3. And a recess 5 is formed centrally of the end face of the roller 3. The recess 5 is formed from both a standpoint of manufacturing the roller 3 and a performance standpoint of the bearing assembly in use. That is, as to the manufacture standpoint, the recess 5 is effective to solve the following problems. If the end face of the roller is not formed with the recess 5 before subjected to grinding, an abrasive stone cannot grind a central portion of the end face, leaving a minor bulge at the central portion. Hence, the subsequent operation of removing the minor bulge is required. What is more, if the minor bulge remains on the end face, it is difficult to establish the roller end face defining a measurement reference plane. This makes it difficult to take measurement on an axial dimension of the roller 3. However, these problems may be solved by forming the recess 5 prior to the grinding process.
As to the performance standpoint, the recess 5 is thought to offer the following advantage. Specifically, the recess 5 stores an oil, which may be supplied to space between the roller end face and the rib 4 by way of centrifugal force associated with the rotation of the roller 3. That is, the recess 5 is designed to serve as an oil reservoir and is thought to be necessary for enhancing lubrication performance.
The conventional roller bearing assemblies have the following constitutions for enhancing the lubrication performance.
As set forth in Japanese Unexamined Patent Publications No. 2004-176771 and No. H7 (1995)-14222, for example, the roller contains a solid lubricant therein. In this constitution, the oil seeping out from an end face of the solid lubricant reduces frictional torque between the rib of the inner ring and the roller. In another constitution set forth in Japanese Unexamined Patent Publication No. 2002-61655, the roller is formed with an axial through-hole and the centrifugal force associated with the rotation of the roller causes the oil (lubricant) to flow through the through-hole so that the oil is supplied to space between the end face of the roller and the rib.